Abstract: Understanding the extent to which a radar view is blocked by surrounding obstacles plays an important role in the proper interpretation of reflectivity data, especially in the lowest antenna elevation angles, which provide the most useful information for rainfall rate estimation at ground level. A terrain based hybrid scan of lowest radar beams that are not significantly blocked by terrain is one of the most important approaches to improve the precision of rainfall estimates. The purpose is to generate hybrid reflectivity field used for precipitation rate calculation from 3-D mosaicked reflectivity field of radar network with high spatial and temporal resolutions. First of all, beam occultation, which is the percent of the radar beam power lost due to beam blockage, is calculated using an algorithm that uses high resolution DEM (digital elevation model) data, radar beam pattern or power density function (Gaussian beam approximation), and radar beam propagation path (assuming radar beams propagate under standard atmospheric refraction conditions). The algorithm begins by remapping Cartesian DEM data to a high resolution polar grid centered on a specified radar location. This high-resolution grid is user defined and used to perform beam occultation calculation. Here, a high grid resolution of 0.1°×250 m is the default setting. Comparison of model calculated beam occultation with radar observations indicates very good qualitative agreement and strongly quantitative correlation. Secondly, hybrid elevation angles are generated using thresholds for beam bottom clearance　(default 150　m) and occultation　(default 60%), which define the criteria for a hybrid elevation angle, which is the lowest angle satisfying both requirements. Beam bottom clearance is the height that a radar beam's bottom passes above the terrain. To compute the hybrid elevation angle, the elevation angle of a beam that clears the terrain by the beam bottom clearance threshold is calculated. The beam occultation is calculated using the elevation angle as a first guess. If the occultation is less than the threshold (60%) then the hybrid elevation has been found. Otherwise, the elevation angle is increased and the beam occultation calculation is performed again. The elevation angle will be adjusted unceasingly in an iterative process (at interval of 0.1°) until finding the hybrid elevation angle. The algorithm is independent of radar types and of radar scan strategies. According to hybrid elevation angle, operational hybrid elevation angle and hybrid scan reflectivity are obtained from volume scan radar data. Then, the standard refractive index beam heights (4/3 earth) are calculated for hybrid elevation angles for every radar in radar network, which are combined to produce a mosaicked beam height map. For the grid cell with multiple radar coverage, the minimum beam height is to be taken. Finally, the hybrid reflectivity field based on the mosaicked beam height field and 3-D mosaicked reflectivity field of radar network is obtained, which is used for rainfall rate estimation at ground level.